Thin-walled Structural Components Research Articles

High precision ultrasonic measurement method for thin-walled parts

Thin-walled parts are extensively utilized in the aerospace industry, where over thinning defects in these parts would significantly compromise mechanical safety. Ultrasound measurement methods are commonly employed for thickness non-destructive testing. Manual calibration of reference signals is usually necessary, negatively impacting automation, robustness, and accuracy. This paper proposes a high-precision ultrasound amplitude method for thin-walled component inspection, getting rid of manual calibration. Firstly, the measured signal is preprocessed to extract the spectrum in the effective frequency range. Then, the spectrum is approximated using the asymmetrical Gaussian amplitude model to estimate the spectrum of reference signal and reflection coefficient. Moreover, initial propagation time is estimated from autocorrelation of the signal. Finally, the accurate thickness is obtained from the numerical calculation of reflection coefficient with the initial time. Simulations and experiments demonstrate that the proposed method can accurately measures metal plates as thin as 0.5 mm. Compared to the traditional correlation method, it greatly improves measurement accuracy and stability, reducing them to 1/2 and 1/4 of the latter, respectively. Additionally, the proposed method also demonstrates high accuracy for curved thin plates, with an average relative error of only 0.57 %. Furthermore, the method exhibits high levels of automation, robustness, and accuracy, and holds significant potential for thickness detection in thin-walled structural components.

Creating Geometric Imperfections in Thin-Walled Structures Using Acoustic Excitation

Abstract Thermomechanical buckling of slender and thin-walled structural components happens without warning and can lead to catastrophic failure. Similar phenomena are observed during plasmolysis (contraction of a plant cell’s protoplast) and rupture of viral capsids. Analytical formulas derived from stability analyses of elastic plates and shells that do not account for the effects of random geometric imperfections introduced during the manufacturing process or biological growth may vastly over-estimate buckling capacity. To ensure structural safety, the formulas must therefore be combined with empirical data to define “knockdown factors” which are in turn used to establish safety factors. Towards improved understanding of the role of imperfections on mechanical response, ingenious methods have been used to fabricate and test near-perfectly hemispherical shells and those containing dimple-like defects. However, a method of inducing imperfections in the form of randomly shaped surfaces remains elusive. We introduce a protocol for realizing such imperfect shells and measuring the pressure required to buckle them. Silicone is poured onto an elastomeric mold under an acoustic excitation, which can be either random sound, or if desired the same as the modal frequency of the mold. Illustrative micro-computed-tomography images and buckling pressure experiments of a nearly perfect shell and an imperfect one show that the method is effective in introducing randomly shaped imperfections of significant magnitudes. This proof-of-concept study demonstrates that the experimental results when combined with computational simulations can lead to improved understanding of stochastic buckling phenomena.

Damage Propagation and Residual Strength of Simple Block-Loaded CFRP Plates with Circular Holes under Tension–Tension Fatigue Conditions

Holes and their effects on the fatigue behavior and damage propagation of thin-walled structural components remain objects of research. In this paper, the previously untreated effect of round holes in thin plain-woven carbon fiber-reinforced plastic plates subjected to simple block loading is examined, and the implication on both damage propagation and residual tensile strength is investigated. Using three-dimensional digital image correlation, the damage propagation in the performed experimental tests is acquired, and the damage size is quantified. The evaluations reveal a relationship between the damage propagation and applied load level, for which an empirical model has been previously established by the authors. As the number of cycles increases, a saturation behavior is found. Once the increased load is imposed on the plate, damage propagation resumes, leading to further damage propagation that can be described with the same empirical model as the initial damage propagation, including renewed saturation behavior. The subsequent experimental tests to determine the residual tensile strength reveal a positive effect of the existing damage size, as the ultimate load significantly exceeds the ultimate load of the non-damaged plate.

Numerical Simulations and Experimental Verification of T-Structure Welding Deformation Using the Step-by-Step Loading Inherent Strain Method

The existing inherent strain method is improved in this paper to address the shortcomings of the existing inherent strain method in the process of loading inherent strain. Unlike the traditional inherent strain method, which uses one-step loading inherent strain for each weld seam for one-time elastic calculation, the improved inherent strain method uses step-by-step loading inherent strain for each weld seam for multiple elastic calculations to predict welding deformation. The step-by-step loading inherent strain method (SBS-ISM) is more in line with the actual welding deformation generation process. Firstly, the local finite element model of the T-joint was used to analyze the welding deformation and extract the inherent strain by using the thermal elastic–plastic finite element method (TEP-FEM). Subsequently, the one-step loading inherent strain method (OS-ISM) and the step-by-step loading inherent strain method (SBS-ISM) were used to predict the welding deformation for the same local finite element model, respectively. The comparative results showed that the trend and magnitude of welding deformation calculated using SBS-ISM was much closer to those calculated using TEP-FEM. The OS-ISM and SBS-ISM were used to predict the welding deformation of the backward centrifugal fan impeller under different welding sequences, respectively. By comparing the welding deformation results calculated using the two inherent strain methods with the experimental results, it was demonstrated that the step-by-step loading inherent strain method (SBS-ISM) provides more accurate and reliable predictions of welding deformation for large and complex thin-walled T-shaped structural components compared to the one-step loading inherent strain method (OS-ISM).

Effects of ply thickness and interference-fit on the bearing strength of single-lap countersunk composite joints

The Countersunk composite joints are widely utilized in the load-bearing components of aerospace structures. However, hole-making causes local stress concentration, affecting joints’ bearing capacity. Therefore, a detailed experimental investigation was conducted on the strength under varying parameters including ply thickness, stacking sequence, and interference size in the single-lap countersunk composite joint. The installation force of the thin-ply joint was smaller than that of the thick-ply at the same interference. The initial damage of the thin-ply hole wall caused by the bolt-inserting process was less. The strengths of the two thick-ply joints improved by 10.12% and 9.09% (1.00% interference), respectively, compared with those of thick-ply neat-fit joints. The strengths of the two thin-ply joints increased by 18.18% and 21.78%, respectively, when the interference was increased to 1.44%. SEM imaging revealed that the damage extent of the thin-ply area is smaller with the same interference. Moreover, the fibre kinking angle of the 0° plies at the thick-ply section was more extensive, leading to fibre fracture. Using interference-fit technology to thin-ply laminates could improve the damage resistance of bolted joints and provide a novel idea for applying thin-ply laminates in thin-walled structural components.

Effect of plastic anisotropy on notch deformation behavior of 7075 high-strength aluminum alloy sheet subjected to axial tension

The notch is an inevitable geometric characteristic in thin-walled structural components. However, the anisotropy in the notch deformation behavior of metal sheets has not been thoroughly investigated. To address this gap, we explored the effect of plastic anisotropy on the notch deformation behavior of the AA7075-T6 sheet subjected to axial tension at room temperature and quasi-static conditions. For this purpose, four types of notched tensile specimens are designed and tested along the rolling, diagonal, and transverse directions. The plastic anisotropy is examined by the dog-bone sample every 15° from the rolling to transverse directions. Full-scale numerical simulations for each notch tensile test were performed in ABAQUS/Standard based on the elastic–plastic constitutive framework with yielding depicted by the Yld2004-18p criterion. The results show that the established numerical models high fidelity reproduced the experimental measurements. It is found that the plastic anisotropy strongly affects the notch deformation of the sheet specimen subjected to axial tension, including strain concentration, plastic localization, stress state, and fracture initiation. Besides, the critical location of cracking in the material depends on the notch geometry parameter w/ρ, viz., the ratio of the half distance between roots of two notch (w) to the radius of the depth notch root (ρ). Another crucial contribution is to provide ideas for a researcher to control or design the path of strain localization by producing metals with specific textures to promote or delay fracture initiation. Accordingly, through the investigation of this work, we provide an essential reference for further engineering applications of high-strength aluminum alloy sheet products with notches.

Static and Dynamic Analysis of Re-Entry Vehicle Nose Structures Made of Different Functionally Graded Materials

High-speed aerospace applications, such as re-entry vehicles, mostly involve thin-walled structural components with a high strength-to-weight ratio and high-temperature resistant. The present novel work comprises the structural and thermal analysis of re-entry vehicle nose structures made of four functionally graded materials (FGM). Four FGM shell structures made of aluminum/silicon carbide, aluminum/aluminum oxide, Ti-6Al-4V/silicon carbide and Ti-6Al-4V/aluminum oxide have been considered for the re-entry vehicle nose. The effect of various thermal environments, as well as the linear temperature rise from metal-rich to ceramic-rich on critical buckling temperature and natural frequency have been studied. The critical buckling temperature, as well as the natural frequency of the large, thin re-entry vehicle nose structures, decrease with an increase in a uniform thermal environment, as well as linear temperature rise. The effect of shell thickness on buckling and dynamic characteristics of an FGM shell is also studied, suiting the nose of the re-entry vehicle under various linear temperature rises. The critical buckling temperature and natural frequency are quantified for several cases, and it was observed that they are significantly influenced by the shell thickness. Thus, the research intends to determine the thickness required for such thin and large shells to withstand in the re-entry thermal conditions.

A hybrid deep learning model for robust prediction of the dimensional accuracy in precision milling of thin-walled structural components

A hybrid deep learning model for robust prediction of the dimensional accuracy in precision milling of thin-walled structural components

Experimental and numerical identification of corrosion degradation of ageing structural components

The study presents experimental and numerical identification of corrosion degradation of thin-walled structural components employing guided wave propagation. The steel structural components are subjected to through-thickness varying corrosion degradation levels. The developed approach using the non-destructive guided wave-propagation quantifies the equivalent average corrosion degradation level by exploring a limited number of transducers. A group velocity dispersion curve reconstruction has been used to determine the corrosion-induced plate thickness reduction. Two case studies are used to examine experimentally the newly developed approach. In the first one, the dispersion curve and the assessment of the corrosion thickness reduction have been made using wave signals of various excitation frequencies. In the second one, the analysis was conducted only for two wave propagation signals and one excitation frequency which allowed for reconstructing the dispersion curve in a limited frequency range. A good agreement between the natural and estimated corrosion degradation levels was observed in both case studies. The present study develops a signal processing methodology, which can be used in the SHM systems. Several aspects still need to be further investigated before the developed approach can be applied to the complex ship hull structures' large size and complex geometry.

Chatter prediction of milling process for titanium alloy thin-walled workpiece based on EMD-SVM

Easy cutting vibration of Titanium alloy thin-walled structural components in processing process directly influences the quality of part machining surface. So, the chatter prediction has become a research hotspot. The milling process of Ti-6Al-4V framework parts for hard alloy cutter is researched and chatter prediction methods are proposed to solve the chatter problem generated in milling process. The signals in milling process are comprehensively considered to work out the stability boundary and the chatter prediction model based on Empirical Mode Decomposition (EMD) and Support Vector Machine (SVM). The stability lobe diagram is utilized to select experiment parameter for experiment, in which the 1/3-2/3 position of framework parts chatters easily in processing. The model training in experiment aims to monitor the time of chatter, with the recognition precision of 97.50%.

Buckling optimization of composite rectangular plates by sequential permutation search with bending-twisting correction

Buckling problem of composite plates is of importance since it is commonly encountered in thin-walled structural components in engineering. Buckling resistance design of composite plates involves the design of laminate stacking sequence exhibiting high dimensional discrete variables owing to the combination and permutation of ply orientations of layers. In this work, a sequential permutation search (SPS) optimization algorithm is presented for the stacking sequence design of composite rectangular plates accounting for the inherent physical-mechanical behavior of composite laminates. Owing to that the governing equation for buckling of composite rectangular plates is a linear homogeneous equation on bending stiffness parameters, the convexity of flexural lamination parameters and sensitivity of bending stiffness are utilized to construct sensitive detection techniques and linear search procedures. Moreover, to increase the robustness of SPS, a sign optimization algorithm (SOA) is coupled in SPS to regulate bending-twisting coupling effects. The SPS algorithm is applied to the buckling resistance design of composite rectangular plates exhibiting various boundaries under axial compression, where the Rayleigh-Ritz method is developed to perform the buckling analysis. Optimal results of SPS are compared against layerwise optimization approach (LOA) and genetic algorithm (GA), illustrating its reliability and efficiency.

Matrix techniques for Lamb-wave damage imaging in metal plates

The implementation of efficient maintenance strategies of thin-walled structural components require reliable damage detection and localization techniques. In particular, guided ultrasonic waves technology represent an auspicious approach when implemented in a structural health monitoring system. The method is usually based on distributed sensing with piezoelectric elements that act in turn as ultrasound transmitter and receiver. This work aims at a unifying framework for damage localization considering algorithms from different scientific disciplines, e.g. originated from radar and geophysics. Here, we systematically express those algorithms in matrix form and compare the respective damage localization performance with experimental measurements considering an isotropic specimen with a single and also multiple simultaneous defects. In addition, we evaluate the algorithms’ point spread function and propose performance metrics to quantitatively compare the imaging success.

Impact response of an origami-shaped composite crash box: Experimental analysis and numerical optimization

In this work, an investigation of the crush response of a simplified CFRP origami crash box subjected to axial impact is proposed. Crash boxes are thin-walled structural components of the vehicles designed to absorb energy during impact events at low-medium velocity. In particular, the crash boxes must guarantee a progressive and controlled energy absorption, avoiding peak of force (and thus acceleration) that can lead to passenger injury. In recent years, crash boxes made of carbon fibre reinforced polymer (CFRP) have found application in the automotive sector. However, their brittle failure mode leads to an irregular crushing trend characterized by peak of force. Thereafter, the crushing behaviour of the composite material structures can be improved by modifying their geometrical parameters. Among the most promising solutions, the origami structure is increasingly considered for crash boxes. The origami crash box here considered consists of four axially stacked basic structures. Each basic structure is composed of four trapezoidal faces and four triangular faces. The upper cross section is squared, whereas the lower cross section has an octagonal shape. The structural behaviour of the origami component was investigated according to different sizes of the triangular faces. The numerical models were simulated with the finite element commercial code LS-Dyna in its explicit formulation. The optimal shape of the origami structure in terms of maximum energy absorption and limited force peak was defined in LS-OPT environment. The objective function of the shape optimization algorithm was set to maximize the energy absorption, while limiting the peak of force. The optimal shape defined presented larger sizes in the top basic structures than in the bottom parts, resulting in more inclined faces. The result suggested that more inclined faces in the top part can guarantee a fracture-triggering effect in the crash box, which ensured a smaller peak force.

Energy Absorption Mechanism of High-Strength Q&P and DP Steel Thin-Walled Structures

In order to research the energy absorption characteristics of high-strength steels in vehicles, the single-hat thin-walled structural components were made from quenching and partitioning (Q&P) steel and dual-phase (DP) steel so as to understand the differences and superiority in the energy absorption characteristics of various types of steel in the energy-absorbing box of current vehicles. Crushing experiments were performed with a testing machine equipped with a high-speed camera. The energy absorption mechanism of the two steels was investigated by means of transmission electron microscopy and electron back-scattered diffraction. The results showed that the energy absorption capacity of Q&P steel is better than that of DP steel, which can be observed from the different compression distances of the single-hat thin-walled structure. The major contribution in energy absorption of Q&P steel comes from the internally retained austenite-to-martensite transformation. The amount of retained austenite substantially reduces at the crushed part with large deformation. On the other hand, while there is a large amount of dislocation and quantity of plug in the crushed DP steel part, the energy stays inside the material without dissipating.

Monolithic and Staggered Strategies Using Solid-Shell Formulations for Nonlinear Coupled Thermoelasticity

AbstractIn this work, monolithic and staggered schemes using a locking-free solid-shell element are proposed to analyze the behavior of thin-walled structural components subjected to combined therm...

Finite element prediction of acoustoelastic effect associated with Lamb wave propagation in pre-stressed plates

The paper presents outcomes of a finite element (FE) study of acoustoelastic effect associated with Lamb wave propagation in plates subjected to homogeneous bi-axial and bending stresses. In particular, the change of the phase velocity of the fundamental Lamb wave modes is obtained for different stress levels, bi-axial stress ratios and wave propagation angles. A comparison of the obtained numerical results with an analytical solution demonstrates a very good agreement. Moreover, the influence of bending stress on the wave velocities and wave front profile is further investigated numerically. There are currently no analytical results for this case. The developed and verified FE modelling approach can help to address several issues in the current non-destructive inspections including: in the investigation of changing stress conditions on the defect detection as well as in an adaptation of the existing Lamb wave-based defect evaluation systems to monitoring of stress too. The latter may have many benefits from sharing the same hardware for the purpose of maintaining structural integrity of thin-walled structural components.

Embedded Acoustic Black Holes for semi-passive broadband vibration attenuation in thin-walled structures

We explore the use of structure-embedded Acoustic Black Holes (ABH) to design thin-walled structural components exhibiting broadband vibration attenuation characteristics. The ABH is a geometric taper with a power-law profile fully integrated into the structural component and able to induce a smooth and progressive decrease of both the velocity and the wavelength of flexural waves. Previous studies have shown these characteristics to be critical to enable highly efficient vibration attenuation systems. The performance of ABH thin-walled structures is numerically and experimentally evaluated under both transient and steady state excitation conditions. Both numerical and experimental results suggest that the proposed approach enables highly efficient and broadband vibration attenuation performance.

Mechanical behaviour of TRC thin-plates exposed to high temperature: experimental study

Textile reinforced concrete (TRC) is a type of composite material with great potential in lightweight and thin-walled structural components bearing high capacity. In this study, TRC thin-plates with epoxy resin impregnated fibre (type 1) and non-impregnated fibre (type 2) were exposed to high temperatures from 35°C to 800°C with the unstressed residual test method. The processed TRC thin-plates were examined through four-point bending tests with the aim of building a foundation for a fire prevention code for TRC. The results demonstrate that the ultimate load of type 1 TRC thin-plates is relatively high and does not vary significantly when the target temperature is below 200°C. The ultimate load of type 2 TRC thin-plates is lower than that of type 1, and does not vary significantly when the target temperature is below 400°C; the turning point for the reduction of ultimate load is 400–500°C, and 20% of loading capacity at normal temperature is maintained at 800°C. Stripping damage to type 1 occurs along the interface and the damage is brittle. For a target temperature of 300°C, epoxy resin is prone to deteriorate and the bursting ratio of the specimens was 100%. The damage feature of type 2 thin-plates is a slipping failure between fibre and mortar mixes, and significant ductile damage properties were observed during the damage process. The investigations were also accompanied by scanning electron microscope and alpha ray spectrometer analyses, which provided an additional basis for analysing the damaged sections of specimens. The results show that the surface flaws of the carbon filaments, matrix decomposition and the weak bond behaviour between the fibres and matrix are affected by elevated temperatures. These three factors may result in the decline of the bearing capacity of type 2 TRC thin-plates.

Analysis of the Collapse Behaviour Regarding TWB Crash-Boxes in Conjunction with the Construction Technique

The crash-boxes are thin-walled structural components with rectangular cross-section which are utilized in the construction of the resistance body structures in the auto industry. This components can be manufactured from various materials including homogenous steel sheet metals, tailor welded blanks (TWB) or even composite materials. The benefits of using TWB were shown in numerous studies before and they are not the main purpose here.This research focuses on the collapse behaviour of TWB thin-walled structures with rectangular cross-section subject of impact loadings. The main objective is to design a crash-box which allows the absorption and dissipation of great kinetic energy constituting better resistance structures for car bodies.After analysing the resulted data, a few aspects regarding the TWB crash-boxes were revealed and some conclusions could be suggested: the weld line generates a barrier like zone which delays in some manner the propagation of the progressive buckling levelling the mean crash load; no flange crash-boxes presented best results regarding the mean crash load even if the data were very close to the other crash-box types. Furthermore, the peak crash load was at maximum level comparing with the other crash-box types. This collapsing behaviour of the no flange crash-boxes could be assigned to the fact that the bonded sides of the structure work like double walls into the same cress-section and is not really affecting the asymmetric crash mode of the structure.

Air Thin-Walled Parts Machining Precision Control

With the development of the aviation industry, the aircraft's increasingly high performance requirements, the overall application of thin-walled structural components became more widespread. However, due to the complex structure parts, thin wall, high precision machining process was complexity, the cutting force, cutting heat, clamping force under the influence of other factors, prone to machining distortion, and with the lower part wall thickness, decreased in rigidity, it was difficult to ensure processing quality. In this paper, we proposed several effective aviation thin-walled parts machining precision control program to solve the problems in the processing of machine structural characteristics of thin-walled parts .The results of experiments and production practice proved that these methods effectively control the air thin-walled parts machining precision machining to meet quality requirements, while reducing the processing time, improve processing efficiency, it was convenient and efficient processing methods.